Periodic Spectral Problems
Lead Research Organisation:
University College London
Department Name: Mathematics
Abstract
Periodic differential operators arise in many areas of physics and mathematics, and studying their spectral properties is very important. Spectra of periodic operators have a band-gap structure, that is, they consist of a collection of closed intervals possibly separated by gaps. There is a famous hypothesis, called the Bethe-Sommerfeld conjecture, which claims that the number of gaps is finite. It has been justified for the Schroedinger operator with an electric field. One aim of the present project is to prove the conjecture in a much more general setting. The solution is expected to require the use of the pseudo-differential calculus, geometry of lattices and geometrical combinatorics. An important quantitative characteristic of differential operators acting on a non-compact manifold in the so-called integrated density of states. This function is a natural analogue of the spectral counting function. We plan to study the behaviour of this function for large values of energy and, in particular, to prove that the density of states has a complete asymptotic expansion in the (negative as well as positive) powers of energy.We also plan to study more basic properties of the nature of the spectrum, namely whether the spectrum is absolutely continuous. We plan to give establish a wide range of sufficient conditions which guarantee the absolute continuity of the spectrum. Finally, we plan to study limit-periodic problems. These problems are natural generalisation of the periodic ones. While the class of limit-periodic operators is not as wide as the class of quasi-periodic or almost-periodic operators, some of the methods of the periodic theory are applicable to the limit-periodic case. We intend to prove the Bethe-Sommerfeld conjecture in the limit-periodic setting.
Organisations
Publications
Artemev A
(2012)
On a class of inverse electrostatic and elasticity problems
Artemev A
(2013)
Inverse electrostatic and elasticity problems for checkered distributions
in Inverse Problems
Barbatis G
(2009)
Bethe-Sommerfeld Conjecture for Pseudodifferential Perturbation
in Communications in Partial Differential Equations
Frank R
(2009)
Weakly coupled bound states of Pauli operators
Frank R
(2010)
Weakly coupled bound states of Pauli operators
in Calculus of Variations and Partial Differential Equations
Kang H
(2009)
DISTRIBUTION OF INTEGER LATTICE POINTS IN A BALL CENTRED AT A DIOPHANTINE POINT
in Mathematika
Laptev A
(2008)
Spectral Theory of Differential Operators
Levitin M
(2010)
Operator Theory and Its Applications
Mityagin B
(2011)
A family of anisotropic integral operators and behavior of its maximal eigenvalue
in Journal of Spectral Theory
Morozov S
(2013)
Complete Asymptotic Expansion of the Integrated Density of States of Multidimensional Almost-Periodic Pseudo-Differential Operators
in Annales Henri Poincaré
Description | We have studied the structure of the spectrum of periodic differential and pseudo-differential operators. We have discovered several important properties, like for example that the Bethe-Sommerfeld conjecture (stating that the spectrum can have only finitely many gaps) holds for a large class of such operators. |
Exploitation Route | The analytical mathematical community can use our results and even more so the techniques developed by us when we were working on this project. The most useful technique that we have developed is the method of the gauge transform the possible applications of which are far from having been exhausted. |
Sectors | Other |
Description | As is common in mathematical research, the results have been disseminated via publications in scientific journals, with preprints made available to the community, as the work progresses, through various electronic archives such as www.arXiv.org. Also as usual, we have presented the ongoing results of our research at various mathematical meetings, conferences and seminar/colloquium talks. |